US Grow Zones

Round Rock, Texas: planting zone & frost dates

Last updated · Sources: PRISM/OSU 2023 ZIP zone listings; NOAA NCEI 1991–2020 Climate Normals (station USC00410433); U.S. Census Bureau — see methodology

Round Rock is in USDA plant hardiness zone 9a, where the average coldest winter night reaches 20 to 25°F (-6.7 to -3.9°C). The typical last spring frost is around Mar 19 and the first fall frost around Nov 13.

Hardiness zone9A20 to 25°F
Last spring frostMar 1930% chance of frost after
First fall frostNov 1330% chance of frost before
Growing season254 daysmedian frost-free days

Frost dates

ProbabilityLast spring frost (32°F)First fall frost (32°F)
Safer (10% risk)Mar 29Nov 3
Typical planning date (30% risk)Mar 19Nov 13
Median (50%)Mar 11Nov 20

How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.

Frost data comes from NOAA station AUSTIN GREAT HILLS, TX (USC00410433), 9.9 mi (15.9 km) from the city center and 148 ft higher than the city center (+45 m). Record used for the 1991–2020 normals: 13 years.

Frost probability in spring and fall, Round Rock, TXChance of a 32°F frost in Round Rock, TX, NOAA 1991–2020. Spring: the chance of another frost falls from 90% on Feb 22 to 10% on Mar 29. Fall: the chance that the first frost has arrived rises from 10% on Nov 3 to 90% on Dec 9.0%50%100%Spring: later frostFeb 1Mar 1Apr 130%: Mar 19Fall: frost arrivedNov 1Dec 1Jan 130%: Nov 1332°F frost28°F hard freezeplanning date
Shaded areas show the chance of a 32°F frost: falling through spring, rising through fall. The dashed line is the 28°F hard-freeze curve. Data: NOAA 1991–2020 Normals, station USC00410433.
Frost-free growing season in Round Rock, TX1 in 10 risk: Mar 29 to Nov 3 (219 days); 3 in 10 risk: Mar 19 to Nov 13 (239 days); Median (50%): Mar 11 to Nov 20 (254 days); No 28°F freeze: Mar 1 to Dec 3 (277 days). In 9 of 10 years the 32°F-free season is at least 230 days.Frost-free days, spring to fallJFMAMJJASOND1 in 10 risk219 days3 in 10 risk239 daysMedian (50%)254 daysNo 28°F freeze277 days
Frost-free window at three risk levels, plus the window between 28°F hard freezes. Read about what the probabilities mean.

Why your yard may differ from the station: microclimates.

Hardiness zone across Round Rock

All 4 ZIP codes covering Round Rock are in zone 9a.

ZIP codes in Round Rock and their zones
ZIPZoneShare of city land
786659a38.7%
786649a31.6%
786819a27.5%
787289a1.1%

Vegetable planting calendar for Round Rock

Dates are counted from the 30%-risk frost dates above (last frost Mar 19, first frost Nov 13). Shift a week later in cold spots or low-lying ground.

CropStart indoorsTransplant / plant outDirect sowFall crop sow/plant
TomatoJan 22 – Feb 5Mar 26 – Apr 9——
PepperJan 8 – Jan 22Apr 2 – Apr 16——
LettuceFeb 5 – Feb 19Mar 5 – Mar 26Feb 19 – Apr 2Sep 4 – Oct 2
Green Beans——Mar 26 – Apr 30Aug 21 – Sep 4
Sweet Corn——Mar 26 – Apr 23—
Zucchini & Summer SquashFeb 19 – Feb 26Mar 26 – Apr 9Mar 26 – Apr 16Aug 21 – Sep 4
CucumberFeb 19 – Feb 26Apr 2 – Apr 9Mar 26 – Apr 16Aug 21 – Sep 4
Carrot——Feb 26 – Apr 2Aug 21 – Sep 4
OnionDec 25 – Jan 8Feb 19 – Mar 5——
Potato—Feb 19 – Mar 12——
BasilFeb 5 – Feb 19Apr 2 – Apr 16Apr 2 – Apr 23—
Spinach——Feb 5 – Mar 5Sep 18 – Oct 16
KaleJan 22 – Feb 5Feb 19 – Mar 12Feb 19 – Mar 12Sep 4 – Oct 2
BroccoliJan 22 – Feb 5Mar 5 – Mar 26—Aug 21 – Sep 4
Peas——Feb 5 – Feb 26Sep 4 – Sep 18
EggplantJan 8 – Jan 22Apr 2 – Apr 16——
CabbageJan 22 – Feb 5Feb 19 – Mar 5—Aug 21 – Sep 4
Radish——Feb 12 – Apr 2Oct 2 – Oct 30
Strawberry—Feb 19 – Mar 12——
Beets——Feb 26 – Apr 9Sep 4 – Sep 18

Nearby cities in Texas

More: all Texas cities · other zone 9a cities: San Antonio, TX, Austin, TX, Seattle, WA, Las Vegas, NV, Portland, OR, Tucson, AZ, Baton Rouge, LA, Tallahassee, FL

Round Rock gardening questions

When is the last frost in Round Rock, TX?

Plan around Mar 19. At NOAA's Austin Great Hills, TX station, 9.9 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Mar 11, and after Mar 29 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Mar 1. The 90% and 10% dates are 35 days apart, close to the 36-day median for cities on this site.

When should I plant tomatoes in Round Rock, TX?

Start seeds indoors Jan 22 – Feb 5 and set transplants outside Mar 26 – Apr 9, once nights stay above 50°F and the soil is near 60°F. That leaves 239 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.

How long is the growing season in Round Rock?

About 254 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 230 days, and in 1 year in 10 it runs 278 days or more. In fall there is a 10% chance of frost by Nov 3 and a 30% chance by Nov 13. That ranks 37th longest of 55 Texas cities on this site.

When should I plant a fall garden in Round Rock?

Count back from the first fall frost (Nov 13): transplant broccoli Aug 21 – Sep 4; sow kale Sep 4 – Oct 2; sow lettuce Sep 4 – Oct 2; sow radishes Oct 2 – Oct 30. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Dec 3. How the math works: succession and fall planting.

Did Round Rock's hardiness zone change on the 2023 map?

Yes. Most of Round Rock was zone 8b on the 2012 map and is zone 9a on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.

How does Round Rock compare with Georgetown, TX?

Both are in zone 9a. The typical last spring frost in Round Rock (Mar 19) comes about 4 days later than in Georgetown, TX (Mar 15), 10 miles away, and the first fall frost is Nov 13 versus Nov 16. The two cities use different NOAA stations.